Trailers fall into two distinctive categories when it comes to classifying them for normal use on the roads of Spain, those below 750kg and those above 750kg maximum weight.
A small trailer, or “Remolque Ligero”, which has a maximum weight less than 750kg does not have to be registered. You must however clearly display the number plate of the vehicle towing the trailer on the rear, which must also be a certified style of number plate, and must have lights fitted which repeat the actions displayed by the towing vehicle.
A larger trailer, which also includes caravans, with a maximum weight over 750kg kilograms, the “Remolque Pesado”, is a different altogether. Firstly, it has to be registered as a separate vehicle and must have its own “Permiso de Circulación”, or log book. It must also have its own registration plate, which is red in colour, and this must be displayed on the rear of the vehicle. This type of trailer is also subject to mandatory testing at an ITV station, and the ITV documents must also be carried with the vehicle. It must also display the number plate of the towing vehicle and have lights on the rear that repeat what the towing vehicle is doing.
There are a couple of points to remember when towing a trailer. Your view of the road must not be obscured, which includes the view in your mirrors. All number plates must be of an officially recognised and certified form, handwritten numbers on cardboard for example are not permitted. If you are towing any form of trailer, you must also carry a fire extinguisher with you in the vehicle.